// JavaScript Document
	var GridRefFigure = 10;
	var GlobalGridSquarePolygon = false;
	var GlobalGridDragLayer = false;
	var GlobalGridSquareClickListener = null;
	var GlobalGridSquareDrawListener = null;
	function RunGetGridRefFromClick(){
	    if(GlobalGridSquareDrawListener != null){
	        GEvent.removeListener(GlobalGridSquareDrawListener);	
		    map.clearOverlays();
	    }
	    
		GlobalGridSquareClickListener = GEvent.addListener(map,"click",function(overlay,latlng){
				map.clearOverlays();
				if(latlng){
					//if(GlobalGridSquarePolygon != false) map.removeOverlay(GlobalGridSquarePolygon);
					//get the scale
					var LatLngBounds = map.getBounds();
					var SouthWest = LatLngBounds.getSouthWest();
					var NorthEast = LatLngBounds.getNorthEast();
					var Scale = SouthWest.distanceFrom(NorthEast);
					//config the grid ref figure
					if (Scale < 110){
						GridRefFigure = 10;
					}else if(Scale > 110 && Scale < 350){
						GridRefFigure = 8;
					}else if(Scale > 350 && Scale < 3000){
						GridRefFigure = 6;
					}else if(Scale > 3000 && Scale < 35000){
						GridRefFigure = 4;
					}else if(Scale > 35000){
						GridRefFigure = 2;
					}
					//alert(Scale);
					//alert(GridRefFigure);
					var OSGrid = GetOSGB(latlng.lat(),latlng.lng());
					//alert(OSGrid);
					//Create the grid square on the map
					var GridSquare = new GetLatLongSquareFromGridRef(OSGrid);
					//alert(GridSquare.lat1);
					var GridSquarePolygon = new GPolygon([
						new GLatLng(GridSquare.lat1,GridSquare.lon1),
						new GLatLng(GridSquare.lat2,GridSquare.lon2),
						new GLatLng(GridSquare.lat3,GridSquare.lon3),
						new GLatLng(GridSquare.lat4,GridSquare.lon4),
						new GLatLng(GridSquare.lat5,GridSquare.lon5),
						], "#f33f00", 3);
					GlobalGridSquarePolygon = GridSquarePolygon; 
					map.addOverlay(GridSquarePolygon);
					var EN = gridrefLetToNum(OSGrid);
					//alert(GridSquarePolygon.getArea());
					//map.setCenter(new GLatLng(GridSquare.lat2,GridSquare.lon2));
					var myHtml = "<br>"+OSGrid+" / "+ EN[0]+","+EN[1]+"<br>Please zoom in or change to<br> satellite view for a more accurate grid reference.";
					map.openInfoWindow(latlng,myHtml);			
				}
			});
	}
	
	var searchResult = false;
	function SearchLocation(SearchTerm,IsGridRef){
		//Search using grid reference
		//var RegGridRef = new RegExp("[A-Za-z]{2}[^\s][0-9]{1,12}");
		//var IsGridRef = RegGridRef.exec(SearchTerm); 
		var result = false;
		if(IsGridRef == true){
			var latlng = convertOSGB36toWGS84(OSGridToLatLong(SearchTerm));
			map.setCenter(new GLatLng(latlng.lat, latlng.lon),14);
			placeMarkerAtPoint(new GLatLng(latlng.lat, latlng.lon));
			searchResult = true;
		}else{
			//Check if postcode
			var RegUKPostcode = new RegExp("^[A-Za-z]{1,2}[0-9A-Za-z]{1,2}[ ]?[0-9]{0,1}[A-Za-z]{2}$");
			var IsUKPostcode = RegUKPostcode.exec(SearchTerm);
			if(!IsUKPostcode){
				//Search using location name
				SearchTerm += ",UK";
				GeoCoder.getLatLng(SearchTerm,function(point){
					if(point){
						map.setCenter(point,14);
						searchResult = true;
					}else{
						alert(SearchTerm +" not found");
						searchResult = false;
					}
				});
			}else{
				//Search using postcode
				usePointFromPostcode(SearchTerm, placeMarkerAtPoint);
				searchResult = true;
			}
		}		
		return searchResult;
	}
	
	function placeMarkerAtPoint(point)
	{
		var marker = new GMarker(point,icon);
		map.setCenter(point, 17);
		map.addOverlay(marker);
	}
	
	function usePointFromPostcode(postcode, callbackFunction) {
		localSearch.setSearchCompleteCallback(null, 
			function() {
				if (localSearch.results[0])
				{		
					var resultLat = localSearch.results[0].lat;
					var resultLng = localSearch.results[0].lng;
					var point = new GLatLng(resultLat,resultLng);
					callbackFunction(point);
				}else{
					alert("Postcode not found!");
				}
			});	
			
		localSearch.execute(postcode + ", UK");
	}
	
	function RunGetGridRefFromDrag(){
	    if(GlobalGridSquareClickListener != null){
	        GEvent.removeListener(GlobalGridSquareClickListener);	
		    map.clearOverlays();
	    }
		
		GlobalGridSquareDrawListener = GEvent.addListener(map,"moveend", function CreateGrid(){
				map.clearOverlays();
				//Get current bound
				//get the scale
				var LatLngBounds = map.getBounds();
				var SouthWest = LatLngBounds.getSouthWest();
				var NorthEast = LatLngBounds.getNorthEast();
				var Scale = Math.round(SouthWest.distanceFrom(NorthEast));
				//config the grid ref figure
				//Debug(Scale);
				
				var GridSize;
				if (Scale < 200){
					GridRefFigure = 8;
					GridSize = 1;
				}else if(Scale > 200 && Scale < 400){
					GridRefFigure = 8;
					GridSize = 10;
				}else if(Scale > 400 && Scale < 3000){
					GridRefFigure = 6;
					GridSize = 100;
				}else if(Scale > 3000 && Scale < 25000){
					GridRefFigure = 4;
					GridSize = 1000;
				}else if(Scale > 25000 && Scale < 106000){
					GridRefFigure = 2;
					GridSize = 10000;
				}else{
				    GridRefFigure = 0;
					GridSize = 100000;
				}
				//Debug("GridRefFigure: "+GridRefFigure);
				//Debug("GridSize: "+ GridSize);
				//Debug("Scale"+ Scale);
					
				// need some calculation here
				// 
				var BottomLeftGrid = GetOSGB(SouthWest.lat(),SouthWest.lng());
				var TopRightGrid = GetOSGB(NorthEast.lat(),NorthEast.lng());
				var BottomLeftXY = gridrefLetToNum(BottomLeftGrid);
				var TopRightXY = gridrefLetToNum(TopRightGrid);
				/*
				if (TopRightXY[0].length == 2){
					TopRightXY[0] += 1000;
					BottomLeftXY[0] += 1000;
				}*/
				//Debug(BottomLeftGrid);
				//Debug(TopRightGrid);
				//Debug(TopRightXY[0]);
				//Debug(BottomLeftXY[0]);
				
				var HorizontalSquareAmount = Math.round((Number(TopRightXY[0])-Number(BottomLeftXY[0]))/GridSize);
				var VerticleSquareAmount = Math.round((Number(TopRightXY[1])-Number(BottomLeftXY[1]))/GridSize);
				//if(VerticleSquareAmount == 0) VerticleSquareAmount = 1;
				//Debug(HorizontalSquareAmount);
				//Debug(VerticleSquareAmount);
				//alert(Scale);
				//alert(GridRefFigure);
				var i = 0;
				var b = 0;
				var NextGridRef = "";
				var NextNorthing=0;
				var SavedStartGrid = "";
				while (b <= VerticleSquareAmount){
					while (i <= HorizontalSquareAmount){
						//alert(SouthWest.lat());
						var OSGrid;
						if(NextGridRef != ""){
							OSGrid = NextGridRef;
						}else{
							OSGrid = GetOSGB(SouthWest.lat(),SouthWest.lng());
						}
						//Debug(OSGrid);
						//alert(OSGrid);
						//Create the grid square on the map
						var GridSquare = new GetLatLongSquareFromGridRef(OSGrid);
						//console.log(GridSquare);
						//Debug(GridSquare.lat1);
						var GridSquarePolygon = new GPolygon([
							new GLatLng(GridSquare.lat1,GridSquare.lon1),
							new GLatLng(GridSquare.lat2,GridSquare.lon2),
							new GLatLng(GridSquare.lat3,GridSquare.lon3),
							new GLatLng(GridSquare.lat4,GridSquare.lon4),
							new GLatLng(GridSquare.lat5,GridSquare.lon5),
							], "#f33f00", 2, 1, "", 0);
							
						map.addOverlay(GridSquarePolygon);
						//GlobalGridDragLayer = GridSquarePolygon;
						//Putting marker onto the map
						var GridRefMarker = new GIcon(G_DEFAULT_ICON);	
						//GridRefMarker.image = "http://localhost:64221/GoogleMaps/GoogleMapLabel.aspx?Label="+ OSGrid;
						GridRefMarker.image = "http://GoogleMaps.record-lrc.co.uk/GoogleMapLabel.aspx?Label="+ OSGrid;
						GridRefMarker.iconSize = new GSize(68,10);
						GridRefMarker.shadowSize = new GSize(0,0);
						GridRefMarker.iconAnchor = new GPoint(-10,15);
						markerOptions = {icon:GridRefMarker};
						var MarkerLatLon = new GLatLng(GridSquare.CenterLat,GridSquare.CenterLon);
						//Debug(GridSquare.CenterGridRef);
						map.addOverlay(new GMarker(MarkerLatLon,markerOptions));
						
						//Generate next square
						var EN = gridrefLetToNum(OSGrid);
						var E = EN[0];
						var N = EN[1];
						//alert(E);
						var NextE = 0; 
						var NextN = 0;
						
						NextE = Number(E)+Number(GridSize);
						NextN = Number(N)
						//Debug(NextE +"/"+ NextN);
						NextGridRef = gridrefNumToLet(NextE, NextN, GridRefFigure);
						//alert(NextGridRef);
						i++;
					}
					i = 0;
					
					//Generate the next verticle grid
					NextNorthing += Number(GridSize);
					
					SavedStartGrid = GetOSGB(SouthWest.lat(),SouthWest.lng());
					var NextVerticleStartGrid = gridrefLetToNum(SavedStartGrid);
					var NextVerticleStartGridE = NextVerticleStartGrid[0];
					var NextVerticleStartGridN = Number(NextVerticleStartGrid[1])+Number(NextNorthing);
					NextGridRef = gridrefNumToLet(NextVerticleStartGridE, NextVerticleStartGridN, GridRefFigure);
					//Debug(NextGridRef);	
					b++;
				}
			});
	}
	function Debug(Message){
		document.getElementById("Message").innerHTML += " "+ Message;
	}
	function Test(){
		//alert("???");
		//window.opener.AddGridReference();
	}
	function GetOSGB(lat,lng){
		var LT = new LatLon(lat,lng,0);
		var OSGB36 = convertWGS84toOSGB36(LT);
		return LatLongToOSGrid(OSGB36);
		//alert(LT.lat); 
	}
	
	function GetLatLongSquareFromGridRef(GridRef){
		var SquareSize = 0;
		switch(GridRefFigure){
		    case 0:
		        SquareSize = 100000;
		    break;
			case 2:
				SquareSize = 10000;
			break;
			case 4:
				SquareSize = 1000;
			break;
			case 6:
				SquareSize = 100;
			break;
			case 8:
				SquareSize = 10;
			break;
			case 10:
				SquareSize = 1;
			break;
		}
		//Debug("SquareSize: "+SquareSize+"/GridRefFigure: "+ GridRefFigure);
		var EN = gridrefLetToNum(GridRef);
		//console.log(EN);
		
		var E = EN[0];
		var N =  EN[1];
		switch(GridRefFigure){
		    case 0:
		        E = E;
				N = N;
			break;
			case 2:
				E = E.substring(0,2)+"0000";
				N = N.substring(0,2)+"0000";
			break;
			case 4:
				E = E.substring(0,4)+"00";
				N = N.substring(0,4)+"00";
			break;
			case 6:
				E = E.substring(0,4)+"00";
				N = N.substring(0,4)+"00";
			break;
			case 8:
				E = E.substring(0,6)+"";
				N = N.substring(0,6)+"";
			break;
		}
		//Debug(GridRef+"/"+E+"/"+N+", "+GridRefFigure+"/"+SquareSize);
		var x1 = E;
		var y1 = N;
		var GridRefXY1 = gridrefNumToLet(x1,y1, GridRefFigure);
		var latlng1 = convertOSGB36toWGS84(OSGridToLatLong(GridRefXY1));
		
		
		var x2 = Number(E)+SquareSize;
		var y2 = Number(N);
		//alert(y2);
		var GridRefXY2 = gridrefNumToLet(x2,y2, GridRefFigure);
		var latlng2 = convertOSGB36toWGS84(OSGridToLatLong(GridRefXY2));
		
		var x3 = Number(E)+SquareSize;
		var y3 = Number(N)+SquareSize;
		//Debug(x3+"/"+y3);

		var GridRefXY3 = gridrefNumToLet(x3,y3, GridRefFigure);
		var latlng3 = convertOSGB36toWGS84(OSGridToLatLong(GridRefXY3));
		
		var x4 = Number(E);
		var y4 = Number(N)+SquareSize;
		var GridRefXY4 = gridrefNumToLet(x4,y4, GridRefFigure);
		var latlng4 = convertOSGB36toWGS84(OSGridToLatLong(GridRefXY4));
		
		var x5 = Number(E);
		var y5 = Number(N);
		var GridRefXY5 = gridrefNumToLet(x5,y5, GridRefFigure);
		var latlng5 = convertOSGB36toWGS84(OSGridToLatLong(GridRefXY5));
		
		var CenterX = Number(x1)+Number(((Number(x2)-Number(x1))/2));
		var CenterY = Number(y1)+Number(((Number(y4)-Number(y1))/2));
		//Debug(CenterX+"/"+CenterY);
		var CenterGridRef = gridrefNumToLet(CenterX,CenterY, GridRefFigure);
		var CenterLatLng = convertOSGB36toWGS84(OSGridToLatLong(CenterGridRef));
		
		this.CenterGridRef = CenterGridRef;
		this.CenterLat = CenterLatLng.lat;
		this.CenterLon = CenterLatLng.lon;
		//Debug(this.CenterGridRef);
		this.lat1 = latlng1.lat;
		this.lon1 = latlng1.lon;
		this.lat2 = latlng2.lat;
		this.lon2 = latlng2.lon;
		this.lat3 = latlng3.lat;
		this.lon3 = latlng3.lon;
		this.lat4 = latlng4.lat;
		this.lon4 = latlng4.lon;
		this.lat5 = latlng5.lat;
		this.lon5 = latlng5.lon;
		//console.log(this);
	}
/*
 * convert geodesic co-ordinates to OS grid reference
 */
 /*
 * construct a LatLon object: arguments in numeric degrees
 *
 * note all LatLong methods expect & return numeric degrees (for lat/long & for bearings)
 */
function LatLon(lat, lon, height) {
  if (arguments.length < 3) height = 0;
  this.lat = lat;
  this.lon = lon;
  this.height = height;
}

function LatLongToEN(p) {
  var lat = p.lat.toRad(), lon = p.lon.toRad();
  //var lat = p.lat, lon = p.lon;
  var a = 6377563.396, b = 6356256.910;          // Airy 1830 major & minor semi-axes
  var F0 = 0.9996012717;                         // NatGrid scale factor on central meridian
  var lat0 = (49).toRad(), lon0 = (-2).toRad();
  //var lat0 = 49, lon0 = -2;  // NatGrid true origin
  var N0 = -100000, E0 = 400000;                 // northing & easting of true origin, metres
  var e2 = 1 - (b*b)/(a*a);                      // eccentricity squared
  var n = (a-b)/(a+b), n2 = n*n, n3 = n*n*n;

  var cosLat = Math.cos(lat), sinLat = Math.sin(lat);
  var nu = a*F0/Math.sqrt(1-e2*sinLat*sinLat);              // transverse radius of curvature
  var rho = a*F0*(1-e2)/Math.pow(1-e2*sinLat*sinLat, 1.5);  // meridional radius of curvature
  var eta2 = nu/rho-1;

  var Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (lat-lat0);
  var Mb = (3*n + 3*n*n + (21/8)*n3) * Math.sin(lat-lat0) * Math.cos(lat+lat0);
  var Mc = ((15/8)*n2 + (15/8)*n3) * Math.sin(2*(lat-lat0)) * Math.cos(2*(lat+lat0));
  var Md = (35/24)*n3 * Math.sin(3*(lat-lat0)) * Math.cos(3*(lat+lat0));
  var M = b * F0 * (Ma - Mb + Mc - Md);              // meridional arc

  var cos3lat = cosLat*cosLat*cosLat;
  var cos5lat = cos3lat*cosLat*cosLat;
  var tan2lat = Math.tan(lat)*Math.tan(lat);
  var tan4lat = tan2lat*tan2lat;

  var I = M + N0;
  var II = (nu/2)*sinLat*cosLat;
  var III = (nu/24)*sinLat*cos3lat*(5-tan2lat+9*eta2);
  var IIIA = (nu/720)*sinLat*cos5lat*(61-58*tan2lat+tan4lat);
  var IV = nu*cosLat;
  var V = (nu/6)*cos3lat*(nu/rho-tan2lat);
  var VI = (nu/120) * cos5lat * (5 - 18*tan2lat + tan4lat + 14*eta2 - 58*tan2lat*eta2);

  var dLon = lon-lon0;
  var dLon2 = dLon*dLon, dLon3 = dLon2*dLon, dLon4 = dLon3*dLon, dLon5 = dLon4*dLon, dLon6 = dLon5*dLon;

  var N = I + II*dLon2 + III*dLon4 + IIIA*dLon6;
  var E = E0 + IV*dLon + V*dLon3 + VI*dLon5;
	//alert(E);
	//alert(N);
  return [E,N];
}

function LatLongToOSGrid(p) {
  var lat = p.lat.toRad(), lon = p.lon.toRad();
  //var lat = p.lat, lon = p.lon;
  var a = 6377563.396, b = 6356256.910;          // Airy 1830 major & minor semi-axes
  var F0 = 0.9996012717;                         // NatGrid scale factor on central meridian
  var lat0 = (49).toRad(), lon0 = (-2).toRad();
  //var lat0 = 49, lon0 = -2;  // NatGrid true origin
  var N0 = -100000, E0 = 400000;                 // northing & easting of true origin, metres
  var e2 = 1 - (b*b)/(a*a);                      // eccentricity squared
  var n = (a-b)/(a+b), n2 = n*n, n3 = n*n*n;

  var cosLat = Math.cos(lat), sinLat = Math.sin(lat);
  var nu = a*F0/Math.sqrt(1-e2*sinLat*sinLat);              // transverse radius of curvature
  var rho = a*F0*(1-e2)/Math.pow(1-e2*sinLat*sinLat, 1.5);  // meridional radius of curvature
  var eta2 = nu/rho-1;

  var Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (lat-lat0);
  var Mb = (3*n + 3*n*n + (21/8)*n3) * Math.sin(lat-lat0) * Math.cos(lat+lat0);
  var Mc = ((15/8)*n2 + (15/8)*n3) * Math.sin(2*(lat-lat0)) * Math.cos(2*(lat+lat0));
  var Md = (35/24)*n3 * Math.sin(3*(lat-lat0)) * Math.cos(3*(lat+lat0));
  var M = b * F0 * (Ma - Mb + Mc - Md);              // meridional arc

  var cos3lat = cosLat*cosLat*cosLat;
  var cos5lat = cos3lat*cosLat*cosLat;
  var tan2lat = Math.tan(lat)*Math.tan(lat);
  var tan4lat = tan2lat*tan2lat;

  var I = M + N0;
  var II = (nu/2)*sinLat*cosLat;
  var III = (nu/24)*sinLat*cos3lat*(5-tan2lat+9*eta2);
  var IIIA = (nu/720)*sinLat*cos5lat*(61-58*tan2lat+tan4lat);
  var IV = nu*cosLat;
  var V = (nu/6)*cos3lat*(nu/rho-tan2lat);
  var VI = (nu/120) * cos5lat * (5 - 18*tan2lat + tan4lat + 14*eta2 - 58*tan2lat*eta2);

  var dLon = lon-lon0;
  var dLon2 = dLon*dLon, dLon3 = dLon2*dLon, dLon4 = dLon3*dLon, dLon5 = dLon4*dLon, dLon6 = dLon5*dLon;

  var N = I + II*dLon2 + III*dLon4 + IIIA*dLon6;
  var E = E0 + IV*dLon + V*dLon3 + VI*dLon5;
	//alert(E);
	//alert(N);
  return gridrefNumToLet(E, N, GridRefFigure);
}


/*
 * convert OS grid reference to geodesic co-ordinates
 */
function OSGridToLatLong(gridRef) {
  var gr = gridrefLetToNum(gridRef);
  var E = gr[0], N = gr[1];

  var a = 6377563.396, b = 6356256.910;              // Airy 1830 major & minor semi-axes
  var F0 = 0.9996012717;                             // NatGrid scale factor on central meridian
  var lat0 = 49*Math.PI/180, lon0 = -2*Math.PI/180;  // NatGrid true origin
  var N0 = -100000, E0 = 400000;                     // northing & easting of true origin, metres
  var e2 = 1 - (b*b)/(a*a);                          // eccentricity squared
  var n = (a-b)/(a+b), n2 = n*n, n3 = n*n*n;

  var lat=lat0, M=0;
  do {
    lat = (N-N0-M)/(a*F0) + lat;

    var Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (lat-lat0);
    var Mb = (3*n + 3*n*n + (21/8)*n3) * Math.sin(lat-lat0) * Math.cos(lat+lat0);
    var Mc = ((15/8)*n2 + (15/8)*n3) * Math.sin(2*(lat-lat0)) * Math.cos(2*(lat+lat0));
    var Md = (35/24)*n3 * Math.sin(3*(lat-lat0)) * Math.cos(3*(lat+lat0));
    M = b * F0 * (Ma - Mb + Mc - Md);                // meridional arc

  } while (N-N0-M >= 0.00001);  // ie until < 0.01mm

  var cosLat = Math.cos(lat), sinLat = Math.sin(lat);
  var nu = a*F0/Math.sqrt(1-e2*sinLat*sinLat);              // transverse radius of curvature
  var rho = a*F0*(1-e2)/Math.pow(1-e2*sinLat*sinLat, 1.5);  // meridional radius of curvature
  var eta2 = nu/rho-1;

  var tanLat = Math.tan(lat);
  var tan2lat = tanLat*tanLat, tan4lat = tan2lat*tan2lat, tan6lat = tan4lat*tan2lat;
  var secLat = 1/cosLat;
  var nu3 = nu*nu*nu, nu5 = nu3*nu*nu, nu7 = nu5*nu*nu;
  var VII = tanLat/(2*rho*nu);
  var VIII = tanLat/(24*rho*nu3)*(5+3*tan2lat+eta2-9*tan2lat*eta2);
  var IX = tanLat/(720*rho*nu5)*(61+90*tan2lat+45*tan4lat);
  var X = secLat/nu;
  var XI = secLat/(6*nu3)*(nu/rho+2*tan2lat);
  var XII = secLat/(120*nu5)*(5+28*tan2lat+24*tan4lat);
  var XIIA = secLat/(5040*nu7)*(61+662*tan2lat+1320*tan4lat+720*tan6lat);

  var dE = (E-E0), dE2 = dE*dE, dE3 = dE2*dE, dE4 = dE2*dE2, dE5 = dE3*dE2, dE6 = dE4*dE2, dE7 = dE5*dE2;
  lat = lat - VII*dE2 + VIII*dE4 - IX*dE6;
  var lon = lon0 + X*dE - XI*dE3 + XII*dE5 - XIIA*dE7;

  return new LatLon(lat.toDeg(), lon.toDeg());
}


/* 
 * convert standard grid reference ('SU387148') to fully numeric ref ([438700,114800])
 *   returned co-ordinates are in metres, centred on grid square for conversion to lat/long
 *
 *   note that northern-most grid squares will give 7-digit northings
 *   no error-checking is done on gridref (bad input will give bad results or NaN)
 */
function gridrefLetToNum(gridref) {
    //Debug("gridref: "+gridref);
  // get numeric values of letter references, mapping A->0, B->1, C->2, etc:
  var l1 = gridref.toUpperCase().charCodeAt(0) - 'A'.charCodeAt(0);
  var l2 = gridref.toUpperCase().charCodeAt(1) - 'A'.charCodeAt(0);
  // shuffle down letters after 'I' since 'I' is not used in grid:
  if (l1 > 7) l1--;
  if (l2 > 7) l2--;

  // convert grid letters into 100km-square indexes from false origin (grid square SV):
  var e = ((l1-2)%5)*5 + (l2%5);
  var n = (19-Math.floor(l1/5)*5) - Math.floor(l2/5);

  // skip grid letters to get numeric part of ref, stripping any spaces:
  gridref = gridref.slice(2).replace(/ /g,'');

  // append numeric part of references to grid index:
  e += gridref.slice(0, gridref.length/2);
  n += gridref.slice(gridref.length/2);
  //alert(e +" "+ n +"/"+gridref.length);
  // normalise to 1m grid, rounding up to centre of grid square:
  switch (gridref.length) {
    case 0: e += '00000'; n += '00000'; break;
	case 2: e += '0000'; n += '0000'; break;
  	case 4: e += '000'; n += '000'; break;
    case 6: e += '00'; n += '00'; break;
    case 8: e += '0'; n += '0'; break;
	// 10-digit refs are already 1m
  }
  //Debug(e +" "+ n);
  
  return [e, n];
}


/*
 * convert numeric grid reference (in metres) to standard-form grid ref
 */
function gridrefNumToLet(e, n, digits) {
  // get the 100km-grid indices
  //n -= n+n; 
  //alert(n);
  var e100k = Math.floor(e/100000), n100k = Math.floor(n/100000);
  //alert(e100k);
  //alert(n100k);
  
  //Out side the UK
  if (e100k<0 || e100k>6 || n100k<0 || n100k>12) return '';

  // translate those into numeric equivalents of the grid letters
  var l1 = (19-n100k) - (19-n100k)%5 + Math.floor((e100k+10)/5);
  var l2 = (19-n100k)*5%25 + e100k%5;

  // compensate for skipped 'I' and build grid letter-pairs
  if (l1 > 7) l1++;
  if (l2 > 7) l2++;
  var letPair = String.fromCharCode(l1+'A'.charCodeAt(0), l2+'A'.charCodeAt(0));
  // strip 100km-grid indices from easting & northing, and reduce precision
  e = Math.floor((e%100000)/Math.pow(10,5-digits/2));
  n = Math.floor((n%100000)/Math.pow(10,5-digits/2));
	
  var gridRef = letPair + e.padLZ(digits/2) + n.padLZ(digits/2);
  if(digits == 0) gridRef = letPair;
  return gridRef;
}

// ellipse parameters
var e = { WGS84:    { a: 6378137,     b: 6356752.3142, f: 1/298.257223563 },
          Airy1830: { a: 6377563.396, b: 6356256.910,  f: 1/299.3249646   } };

// helmert transform parameters
var h = { WGS84toOSGB36: { tx: -446.448,  ty:  125.157,   tz: -542.060,   // m
                           rx:   -0.1502, ry:   -0.2470,  rz:   -0.8421,  // sec
                           s:    20.4894 },                               // ppm
          OSGB36toWGS84: { tx:  446.448,  ty: -125.157,   tz:  542.060,
                           rx:    0.1502, ry:    0.2470,  rz:    0.8421,
                           s:   -20.4894 } };


function convertOSGB36toWGS84(p1) {
  var p2 = convert(p1, e.Airy1830, h.OSGB36toWGS84, e.WGS84);
  return p2;
}


function convertWGS84toOSGB36(p1) {
  var p2 = convert(p1, e.WGS84, h.WGS84toOSGB36, e.Airy1830);
  return p2;
}


function convert(p, e1, t, e2) {
  // -- convert polar to cartesian coordinates (using ellipse 1)
  
  p1 = new LatLon(p.lat, p.lon, p.height);  // to avoid modifying passed param
  p1.lat = p.lat.toRad(); p1.lon = p.lon.toRad(); 

  var a = e1.a, b = e1.b;

  var sinPhi = Math.sin(p1.lat), cosPhi = Math.cos(p1.lat);
  var sinLambda = Math.sin(p1.lon), cosLambda = Math.cos(p1.lon);
  var H = p1.height;

  var eSq = (a*a - b*b) / (a*a);
  var nu = a / Math.sqrt(1 - eSq*sinPhi*sinPhi);

  var x1 = (nu+H) * cosPhi * cosLambda;
  var y1 = (nu+H) * cosPhi * sinLambda;
  var z1 = ((1-eSq)*nu + H) * sinPhi;


  // -- apply helmert transform using appropriate params
  
  var tx = t.tx, ty = t.ty, tz = t.tz;
  var rx = t.rx/3600 * Math.PI/180;  // normalise seconds to radians
  var ry = t.ry/3600 * Math.PI/180;
  var rz = t.rz/3600 * Math.PI/180;
  var s1 = t.s/1e6 + 1;              // normalise ppm to (s+1)

  // apply transform
  var x2 = tx + x1*s1 - y1*rz + z1*ry;
  var y2 = ty + x1*rz + y1*s1 - z1*rx;
  var z2 = tz - x1*ry + y1*rx + z1*s1;


  // -- convert cartesian to polar coordinates (using ellipse 2)

  a = e2.a, b = e2.b;
  var precision = 4 / a;  // results accurate to around 4 metres

  eSq = (a*a - b*b) / (a*a);
  var p = Math.sqrt(x2*x2 + y2*y2);
  var phi = Math.atan2(z2, p*(1-eSq)), phiP = 2*Math.PI;
  while (Math.abs(phi-phiP) > precision) {
    nu = a / Math.sqrt(1 - eSq*Math.sin(phi)*Math.sin(phi));
    phiP = phi;
    phi = Math.atan2(z2 + eSq*nu*Math.sin(phi), p);
  }
  var lambda = Math.atan2(y2, x2);
  H = p/Math.cos(phi) - nu;

  return new LatLon(phi.toDeg(), lambda.toDeg(), H);
}


/*
 * pad a number with sufficient leading zeros to make it w chars wide
 */
Number.prototype.padLZ = function(w) {
  var n = this.toString();
  for (var i=0; i<w-n.length; i++) n = '0' + n;
  return n;
}
Number.prototype.toRad = function() {  // convert degrees to radians
  return this * Math.PI / 180;
}
Number.prototype.toDeg = function() {  // convert radians to degrees (signed)
  return this * 180 / Math.PI;
}

function copy(inElement) {
  if (inElement.createTextRange) {
    var range = inElement.createTextRange();
    if (range && BodyLoaded==1)
      range.execCommand('Copy');
  } else {
    var flashcopier = 'flashcopier';
    if(!document.getElementById(flashcopier)) {
      var divholder = document.createElement('div');
      divholder.id = flashcopier;
      document.body.appendChild(divholder);
    }
    document.getElementById(flashcopier).innerHTML = '';
    var divinfo = '<embed src="Images/_clipboard.swf" FlashVars="clipboard='+encodeURIComponent(inElement.value)+'" width="0" height="0" type="application/x-shockwave-flash"></embed>';
    document.getElementById(flashcopier).innerHTML = divinfo;
  }
}